Most SONET transmission systems use some form of line-level protection facility (such as those known as “1+1”, “1:1”, “1:n”) in order to provide a high degree of reliability for data transport. These protection facilities provide a level of certainty that data transport will continue in the event of a line failure, but the known facilities are not able to prevent temporary interruptions of service.
SONET systems typically monitor the working line and, if and when a certain number of data frame defects are detected within a predetermined amount of time, the system switches over to another transmission line which is referred to as a protection line. Normally it takes in the order of tens of milliseconds from the point in time that the first defect is detected to the point at which data traffic on the protection line is restored. At the gigabit data transmission speeds of fibre channel (FC) links such a switching time period may represent in the order of several thousands of data frames. During this period corrupted data frames may be transported to the fibre channel client receiver and this may cause performance degradation or link failure due to fact that the receiving equipment may incorrectly account for corrupted frames and cause the buffer-to-buffer credit count between the sending and receiving equipment to become incoherent.
One method of addressing this problem is to buffer the received data frame as it is de-encapsulated, since most encapsulation protocols have a CRC or checksum field which can be used to validate frame integrity, discarding those frames detected as corrupt. However, this method presents disadvantages in that it causes the frame to incur latency and requires buffering a frame of up to 2200 bytes.
There is a need, therefore, for means to enable an efficient detection and handling of corrupted frames prior to the transmission thereof over a protected line to a client receiver.